As the density of semiconductor devices increases, the importance of the technologies for forming multilayer wires, interlayer insulating films which accompany and electrodes, such as plugs and damascene electrodes, has been increasing. Together with this, the importance of the flattening process for these interlayer insulating films and metal films of the electrodes has been increasing and a polishing technology, which is referred to as CMP (chemical mechanical polishing), has been spreading as an efficient technology for this flattening process.
As for the polishing apparatus using this CMP technology, an apparatus for measuring the polished state by irradiating the polished surface of a substrate, such as a wafer, with a laser beam or visible light from the rear surface of the polishing pad (on the platen side) while polishing the substrate, as shown in FIG. 1, has been attracting attention as being technologically important (see Japanese Unexamined Patent Publication H9 (1997)-7985).
As a polishing pad for detecting the final point which is used in this polishing apparatus, a polishing pad which is useful for polishing wafers on which integrated circuits are mounted and at least a portion of which is made of a hard uniform resin sheet having no essential performance of absorption or transportation of slurry particles where a light beam having a wavelength in a range from 190 nanometers to 3500 nanometers transmits through this resin sheet is introduced (see Japanese Translation of International Unexamined Patent Publication H11 (1999)-512977).
A typical example of such a polishing pad is IC-1000, made by Rohm and Haas Company, and the transmittance of light of the polishing layer made of a foam structure containing micro-balloons (micro-capsules) is insufficient and, therefore, this polishing pad has a polishing layer and a cushion layer which is layered on the above described polishing layer via a double-sided adhesive tape or the like, and an opening which penetrates through all of the above described polishing layer, double-sided adhesive tape and cushion layer is created in a predetermined location of the above described polishing pad, and a Window member made of a thermosetting hard, uniform resin which is solid and transparent is fit into the above described opening from the polishing surface side. This is a structure as shown in FIG. 2.
In the polishing pad having such a transparent, hard, uniform resin as a window member, however, the window member makes contact with the surface of the substrate having a surface to be polished and, therefore, there are problems where the surface of the substrate is easily scratched, the slurry leaks due to the peeling of the window member, and the detection of the final point fails due to the protrusion of the window member in the upward direction from the polishing surface caused by the expansion of air surrounded by the window member and the platen when the temperature rises while polishing. In addition, there is a problem where a manufacturing process becomes complicated due to the difference in the form of the openings created in the polishing layer and the cushion layer. Furthermore, there is a problem with the process where the molding cycle time becomes long in the manufacture of the thermosetting hard, uniform resin.
Meanwhile, methods for polishing a wafer according to which through holes are provided in the polishing pad and the polished state is determined by viewing the state of reflection of light from the polished surface of a wafer are known (see Japanese Unexamined Patent Publication 2000-254860). As for the two types of through holes introduced herein, however, an end of one through hole is close to the center of the polishing pad and, therefore, slurry supplied from the center of the polishing pad goes into the through hole and stays there, and a problem arises where a sufficient amount of light does not pass through while the length of another through hole in the direction perpendicular to the direction of the center of the pad is too long for the wafer and, therefore, a problem arises that the workpiece cannot be polished uniformly.
In view of that background, it could be helpful to provide a polishing pad and a polishing apparatus where the polishing pad is used to form a planar surface on glass, semiconductors, dielectric material/metal composites and integrated circuits, it is difficult for the surface of the substrate to be scratched, the polished state can be appropriately measured optically during polishing, and whether or not the entire surface of the workpiece can be polished uniformly can be measured.